Patients with the autosomal recessive disease, Familial Mediterranean fever (FMF), suffer periodic, upredictable attacks of fever associated with severe pain; the pain is localized most commonly in joints (arthritis), abdomen (peritonitis) or chest (pleuritis). Occasionally, this disease presents with skin manifestations (erysipeloid erythema), pericarditis, vasculitis, or myalgia. In many patients, amyloidosis is a complication, and if untreated, this can be life-threatening. FMF is caused by missense mutations in pyrin, a protein of unknown function expressed in neutrophils, monocytes, eosinophils, dendritic cells, synovial cells and skin and peritoneal fibroblasts. Pyrin expression in these cells is induced by pro-inflammatory cytokines and by LPS. Thus, it has been speculated that pyrin modulates the inflammatory response. Evolutionary studies of the pyrin molecule indicate that it has been under positive Darwinian selection during evolution of the primates. Moreover, the high frequency of mutant pyrin alleles in several human ethnic groups supports a heterozygote (selective) advantage for the mutant allele. Mutant forms of pyrin may enhance the body's ability to clear important pathogen(s). Indeed, acute phase reactants, important agents of innate immunity, are up-regulated not only in patients but in carriers of mutant alleles. Structural analysis of the pyrin molecule revealed that exon 1 encodes a death-domain related structural motif (known as the pyrin domain or PyD) that is found in a growing family of proteins involved in inflammation and innate immunity. Identification of pyrin-interacting proteins as well as additional functional studies reveal that pyrin is linked directly to apoptotic and cytoskeletal signaling cascades, and that it modulates cytokine secretion. Experiments described in this proposal are designed to further explore these functions of pyrin and determine the effects of pyrin mutations on apoptosis (Aim 1); cytoskeletal signaling (Aim 2); and cytokine production (Aim 3). Recently identified pyrin isoforms will also be examined in these functional assays, since preliminary studies indicate that the various isoforms may function differently. Such studies could provide clues to understanding of the molecular pathogenesis of FMF, and may reveal new information about inflammatory pathways in general. In fact, pyrin-interacting proteins and pyrin domain-containing family members have already been connected to several human diseases, including inflammatory bowel disease, PAPA syndrome, Muckle-Wells sydrome, familial cold urticaria, Blau syndrome and Be_het's disease.